Edison’s High Resistance Platinum Lamp, 1879.
This lamp had a high resistance burner, necessary for the multiple system.
Edison’s High Resistance Platinum in Vacuum Lamp, 1879.
This experimental lamp led to the invention of the successful carbon filament lamp.
During his experiments he had found that platinum became exceedingly hard after it had been heated several times to incandescence by current flowing through it. This apparently raised its melting temperature so he was able to increase the operating temperature and therefore greatly increase the candlepower of his lamps after they had been heated a few times. Examination of the platinum under a microscope showed it to be much less porous after heating, so he reasoned that gases were occluded throughout the platinum and were driven out by the heat. This led him to make a lamp with a platinum wire to operate in vacuum, as he thought that more of the occluded gases would come out under such circumstances.
Edison’s Carbon Lamp of October 21, 1879.
This experimental lamp, having a high resistance carbon filament operating in a high vacuum maintained by an all-glass globe, was the keystone of Edison’s successful incandescent lighting system. All incandescent lamps made today embody the basic features of this lamp. This replica is in the Smithsonian Institution exhibit of Edison lamps. The original was destroyed.